Applying the Proper Characterization of LEDs with Average LED Intensity (ALI)
Luminous intensity measurements assume an object appears as a point source. For example laser diodes are microns in size and are point sources. However, white LEDs are large; about 1,000 times larger than laser diodes, more than 1 millimeter. To appear as a point source the white LED would need to be measured over longer distance i.e. meters. This increase in distance produces lower luminance intensities, which requires longer measurement times to compensate.
LED manufactures need short measurement times to increase throughput. Thus, manufactures and CIE devised a new test condition named Averaged LED Intensity (ALI). ALI ensures that all manufactures measure at the same conditions and have a short measurement time. Results between manufactures can then be directly compared, even if the LED does not appear as a light source.
Concept of CIE 127:2007
“Condition B” is the most commonly used configuration. The LED is positioned 100mm from a round detector with an active area of 1 cm².
Instrument Systems LED-43X series holds the LED at the correct position and precisely couples the light into a spectrometer like the CAS-140CTS or SP320. Different mechanical adapters are available to allow alignment to a variety of LED handling machines.
For higher precision measurements the LED25-100 measures average LED intensity using a tiny 25mm integrating sphere inside.
Figure 1: shows the LED-430 measuring adapter that conforms to the standard CIE condition B for 100 mm distance.
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